DESCRIPTION (provided by Principal Investigator): Adult teleost fish and urodele amphibians have the capacity to regenerate entire amputated appendages. In striking contrast, regenerative healing of mammalian limbs is limited to the very tips of digits. During limb regeneration in urodeles and fin regeneration in teleosts, regeneration is precisely regulated such that only the appropriate structures are replaced. One of the classic and unexplained questions of appendage regeneration is how adult cells in the injured area retain or recognize the positional information necessary to accomplish this. The central questions by which this positional memory is maintained are these. First, to what extent do cells retain their lineage restriction and state of differentiation during regeneration? That is, are differentiated adult cells of one lineage able to contribute to one or more other lineages, or to assume a less differentiated form? Second, which specific molecular programs are essential for retaining and regulating positional information within these cells? Here, we propose to define new cellular and molecular regulatory mechanisms that maintain positional information and instruct regenerative renewal of zebrafish fins, complex organs containing bone, connective tissue mesenchyme, epidermis, blood vessels, nerves, and pigment cells. In this proposal, we describe a programmatic approach to positional memory, using 1) new technology for the lineage tracing of adult fin cells; 2) candidate gene testing based on new results; and 3) a forward genetic approach of mutagenesis screening and positional cloning. With this approach, we will test the hypothesis that differentiated adult appendage tissues express region-specific profiles of regulatory factors that maintain positional information important for regenerative fidelity. Our molecular genetic approach will increase understanding of regulatory mechanisms active during regenerative organogenesis, and provide important perspective for comprehending, and perhaps changing, the existing limitations in regenerative capacity of most human organs.